In a preliminary investigation, a significant number of blood cultures obtained from patients with acute and recurrent thromboembolic disease were positive for gram-negative non-sporulating anaerobic microorganisms and organisms of "L-type" morphology. Blood cultures obtained from a group of control individuals, who had no evidence of infection or thrombophlebitis, were consistently negative. We have proposed to study 60 patients with idiopathic acute or recurrent thromboembolic and an equal number of control individuals to determine if there is an association between bacteremia with members of the family Bacteroidaceae or organisms of "L-type" morphology and thromboembolic disease. We will also determine if there are clinical features unique to those patients with blood cultures positive for these microorganisms. In addition, the mechanisms by which cell wall components of gram-negative anaerobic microorganisms affect coagulation and the host's response to bacteremia with members of the family Bacteroidaceae will be investigated.